A sensor to indicate movement of an object may be created using the so-called “Hall effect” wherein an electric value in a conductor is changed due to the movement of a proximal magnetic field. For example, U.S. Pat. No. 4,392,375 to Eguchi et al., discloses two spaced apart permanent magnets rotatable about a magnetic sensing element.
U.S. Pat. No. 5,818,223 to Wolf discloses a single rectangular magnet positioned adjacent to and rotatable relative a magnetic sensing element. Bookend-shaped flux concentrators on two sides of the magnetic sensing element are used to concentrate the flux. In an attempt to reduce the axial length of the sensor, in another disclosed embodiment, a ring-shaped magnet is used and a similar arrangement including a sensing element sandwiched between flux concentrators is located within the ring-shaped magnet. The axial positioning of the magnetic sensing element for this device is critical, and steps are taken to try to ensure central location thereof by including a separate nonmagnetically conducting housing with a center locating well to hold the sensor/concentrator arrangement. Proper axial location is further attempted by defining a notch to receive the sensing element at the bottom of the well.
Both described devices have disadvantages including: only one magnetic sensing element may be used; as discussed, the magnetic sensing element must be centrally located; any divergence from the center may affect the accuracy of the sensor; the magnetic elements do not use magnetic material as effectively as the current invention; and reducing the overall size of the disclosed devices is limited.
In the case of the Wolf device, assembly of the sensor may be problematic as proper orientation cannot be assured due to the radial symmetric magnet. Attempts to overcome possible misorientation of the generally circular magnets may include magnetizing the magnetic material to the proper orientation after it has been assembled. This has the disadvantage however in that the magnetic material is predisposed to be oriented to a particular direction. Any variance from the particular direction is less than optimal.